This invention relates to a video printer which prints a screen image on a sheet of print paper, and particularly to a signal processor for a video printer having a sampling circuit which extracts print data from a video signal.
A conventional video printer has its sampling circuit designed to convert an analog video signal directly into digital data and store the data temporarily in a memory, and it reads the print data out of the memory for printing, as described in JPA No. 58-138667. Therefore, an input video signal at a higher frequency is stored in the memory at an increased data rate, accordingly. Namely, the conventional technique solely copes with an increased frequency of the video signal by speeding up the operation of the sampling circuit and memory.
On this account, the sampling circuit and memory are required to operate faster as the horizontal scanning frequency is raised. In the case of a high-resolution display in which the video signal has a horizontal scanning frequency of 64 kHz, for example, the video signal frequency reaches 100 MHz, at which frequency the A/D converter for the video signal and the associated sampling circuit including a write clock generator must operate. However, it is difficult to design such a fast sampling circuit, and the circuit will be complex and expensive.